1. Field of the Invention
The present invention relates to a secondary loop cooling system for use with a vapor compression air conditioning system, and a method for bypassing a reservoir in such a system. In particular, the cooling system uses a non-flammable cooling fluid, which is particularly useful when the refrigerant used in the vapor compression system is flammable.
2. Description of Related Art
New environmental regulations on working fluids have forced the refrigeration and air-conditioning industry to look for new working fluids with low global warming potential (GWP). Replacement working fluids are being sought that have low GWP, no toxicity, non-flammability, reasonable cost and excellent performance.
HFC-152a (1-1) difluoroethane, a flammable refrigerant, is being considered for a secondary loop system in a mobile air conditioning system to prevent it from leaking into the passenger compartment. Such secondary loop systems are known. A typical, known mobile air conditioning system is shown in FIG. 1. This system, shown generally at 10, includes a primary vapor compression system, which may be used as a mobile air conditioning system, shown generally at 20 in FIG. 1, and a secondary loop cooling system, shown generally at 30 in FIG. 1. With reference to FIG. 1, the vapor compression system includes a compressor 11 having an inlet 12 and an outlet 13, and an optional accumulator 14 having an inlet 15 and an outlet 16. A connecting line 17 connects the accumulator and the compressor. If the accumulator is used, it separates any liquid which is not evaporated in the heat exchanger and prevents the liquid from entering the compressor. A gaseous refrigerant flows from outlet 16 of accumulator 14 and through connecting line 17 to an inlet 12 of compressor 11, where the gaseous refrigerant is compressed to a higher pressure. Outlet 13 of the compressor is connected by a connecting line 18 to a condenser 19, which has an inlet 21 and an outlet 22. The compressed gaseous refrigerant is circulated from line 18 to inlet 21 and through the condenser, thus giving off heat, and is converted to a liquid in the condenser. The liquid refrigerant is circulated to outlet 22 of the condenser and through an expansion device in a connecting line 24 which connects the condenser to a chiller, or heat exchanger, 25, which is part of the cooling system 30. Heat exchanger 25 includes a first expansion coil, or tube, 26 having an inlet 27 and an outlet 28. The refrigerant circulates from inlet 27, through the expansion coil, and to outlet 28. The liquid refrigerant flows through the first expansion coil of the heat exchanger and expands. Heat exchanger 25 also includes a second expansion coil, or tube, 29 having an inlet 31 and an outlet 32 for circulating a cooling solution therethrough. The liquid refrigerant evaporates in the heat exchanger at a low temperature to form a low pressure gas and thus produces cooling of the cooling solution. Outlet 28 of the first expansion coil of the heat exchanger is connected by a connecting line 34 to inlet 15 of the accumulator. The low-pressure refrigerant gas from the heat exchanger enters the compressor where the gas is compressed to raise its pressure and temperature, and the cycle then repeats.
The cooling solution in second expansion coil 29 of the heat exchanger is circulated from outlet 32 of the second expansion coil through a connecting line 35 to a cooling unit 33, which has an inlet 36 and an outlet 37. The cooling solution is circulated to inlet 36 of the cooling unit, through the cooling unit and to outlet 37 thereof. The cooling unit is located in the passenger compartment. A fan, not shown, is disposed outside of the cooling unit, and the air from the fan passing across the cooling unit provides cooling to the passenger compartment. The cooling solution is then circulated to a reservoir 38 via a connecting line 39. The reservoir has an inlet 40 and an outlet 41. The cooling solution is pumped to inlet 40, through the reservoir, and to outlet 41 and out of the reservoir to a pump 43 through a connecting line 42, which connects the reservoir and the pump. The pump has an inlet 44 and an outlet 45, and the cooling fluid flows from inlet 44 through the pump to outlet 45 and is pumped back to inlet 31 of the second expansion coil of the heat exchanger via a connecting line 46.
One of the drawbacks with such a secondary loop system is the relatively slow cool down of the passenger compartment of an automobile, especially on a hot day as compared to use of only a primary vapor compression system, such as that shown at 20 in FIG. 1. Therefore, there exists a need to expedite the cooling of the passenger compartment of an automobile with a secondary loop cooling system.